1. Technical Field
The invention relates to a method of detecting the particles of a tobacco particle stream in the production of smokable articles, in particular of winnowings.
In cigarette production, the incoming tobacco stream in the cigarette maker is screened. Only sufficiently fine material is incorporated in the bundle. The remaining portion of the more coarse material, the so-called xe2x80x9cwinnowingsxe2x80x9d, is eliminated by the screening process and is collected centrally by pneumatic transport for further processing.
In order to optimize operation of the cigarette maker, it is important to determine online the mass stream of winnowings to and in operation of the cigarette maker as well as the size distribution of the winnowings, and to make use of the resulting parameters in adjusting separation of the winnowings. Up until now, detection of the winnowings was not effectuated at the cigarette maker, instead (if at all performed) it was carried out offline by sieve analysis of the eliminated winnowings. The ensuing measured results may then serve to optimize the screening conditions online as regards high product quality (elimination of practically all winnowings), i.e. by exclusively eliminating winnowings. However, optimization would be quicker and more flexible if analysis of the winnowings mass stream would be possible online directly at the winnowings exit of the cigarette maker. Measuring the mass stream in this way must take place at variable velocity of the transport air stream so that proper functioning is also assured given changing operation parameters of the cigarette maker, and the accuracy of the measured results should be independent of fluctuations in the particle size of the winnowings. In addition, it is of interest for continuous process monitoring to obtain information as to the momentary size distribution from the winnowings particle stream, for instance as regards the average particle size and the spread of the size distribution so as to be able to recognize quickly and selectively malfunctioning of the screening process.
This is, by definition, not possible with offline sieve analysis employed up to now.
2. Description of Related Art
In other technical fields outside of cigarette production, various optical screening methods have already been developed. Thus, patent DE 41 19 240 C2 discloses a method of determining the particle size distribution of a particle mixture in which the individual particles have a spherical shape. The particle mixture moves past an optoelectronic measuring length perpendicular to a parallel light beam and is optoelectronically scanned linewise. The chord lengths of the particles are measured and are assigned specific length classes by a classifier; from which the particle size distribution is computed in accordance to particle size classes defined according to the particle diameters of the corresponding length classes.
As the shapes of the winnowings greatly differ from spherical shapes, this method cannot be implemented for screening tobacco particles.
Patent DE 32 36 261 describes a method of determining the average radius and/or the average length of particles transported in a stream medium which fly through two slots of a mask. The beam emitted, dispersed or absorbed by the particles in passing through these slots is monitored to thus enable certain particles to be identified which have fully passed through both slots. This method is also not suitable for screening tobacco winnowings due to their irregular shapes.
A similar method is disclosed by patent DE 197 06 890 A, in which the particles are identified for which the emitted, dispersed or absorbed beam has a predefined relationship; the size of the identified particles is determined from the amount of emitted, dispersed or absorbed beams when the identified particles pass through the slots.
Patent DE 37 06 502 discloses a device for determining the grain distribution of a powdery product using two measuring cells which may be introduced in the beam path of a laser beam alternately so that one measuring cell is available for operation while, simultaneously, the second measuring cell is being cleaned.
Patent DE 42 15 908 A discloses an optical particle measuring method for clean room monitoring and for keeping a check on high-purity fluid, in which the particles directed through the measured volume are beamed and an imaging device, including a detector, detects the resulting diffused light; the radiation for the measured volume is modulated such that a measuring signal, modulated in time, materializes and renders possible improvement of the signal-to-noise ratio.
Patent DE 28 55 583 C2 describes a method for determining the grain distribution of grain mixtures which are statically recorded by means of a TV camera and the data is processed as a function of the statically projected images of the falling grains. Calibration measurements are made on a sieved-out grain class from the grain mixture, and under the assumption that the grains have the configuration of an ellipsoid of rotation, an average configuration coefficient is determined as the average value of the relationship of the longitudinal axis to the short axis of the grains. This shape assumption of an ellipsoid of rotation is likewise not applicable to tobacco particles.
Shown in patent 32 16 486 is a detector for the trimmed surplus tobacco in cigarette production. All of the trimmed surplus tobacco is pneumatically passed through the detector, the light beam of which is dimmed by the tobacco stream in a similar manner as a screen. The strength of the current generated by the photocells of the detector is thus inversely proportional to the density of the tobacco stream, and thus to the tobacco throughput. The detection of individual tobacco particles is not possible.
In conclusion, patent DE 43 07 407 C2 discloses a device for producing cigarettes in which the light tobacco particles are separated from the waste material with the heavier tobacco particles. There is no mention of monitoring the quality of separation using a suitable sensor.
An object of the invention is to provide a method of detecting the mass stream of particles of a winnowings stream in the production of smokable articles, which overcomes the disadvantages of subsequent sieve analysis. In particular, a method is proposed which works online and can thus be employed to optimize the screening conditions as regards product quality and the elimination of winnowings exclusively.
This objective is achieved by the features set forth in claim 1.
Expedient embodiments are defined by the features of the sub-claims.
The advantages achieved by the invention are based on an optical method which functions by using a fine-beam light barrier and detects from the darkening of the light beam of the fine-beam light barrier an average dimension and an average volume of the winnowings particle based statistical considerations.
This measurement furnishes primarily information on the particle size distribution, since the individual particles are measured separately, from which the average dimension, the average volume, the average particle mass and the particle mass stream are continuously determined.
The measured value thus obtained for the mass stream is independent of the transporting velocity of the winnowings stream since the particle velocity is directly measured in the device, for example, by employing a second fine-beam light barrier, and in computing the aforementioned parameters. In this way, the slip of the particles in the stream is also taken into account and the measuring device is self-sufficient, independent of other sensors.
Measuring is achievable without any complicated designs for the input and output of the winnowings stream, simply by transporting the winnowings stream, extracted from the cigarette maker, through a transporting/sensor tube on which the or each fine-beam light barrier is arranged. The necessary overall height required is less than 100 mm so that space should remain available everywhere for installing this sensor.
This optical measuring method results in no additional degradation of the winnowings stream, since the sensor works contact-free, and can be inserted with zero impact and with no change in cross-section directly into an existing transport tube which may directly serve as the sensor tube.
The relatively straightforward configuration of the mechanical/physical part of the sensor ensures high reliability coupled with a relatively low price, especially when buying in bulk.